Effect of Sodium-mixed Anion Doping in PEO-based Polymer Electrolytes

Three poly(ethylene oxide) based sodium ion-conducting mixed anion systems, namely. PEO: (1 - x) NaI + xNaSCN, PEO:(1 - x) NaI + xNaCH(3)COO, PEO:(1 - x) NaSCN + xNaCH(3)COO have been studied. The characteristic dip in conductivity isotherm for all the three systems was observed below and above the melting of the complex. The isolated cation transference number has also been reported by the combined a.c.-d.c. technique for all three systems. The value of t(Na+) was found to be modified due to mixed anion doping. The detailed analysis of the systems under optical microscopy, differential scanning calorimetry, complex impedance spectroscopy and dielectric constant is discussed in the paper. It is shown that the mixed anion doping in polar-non polar combination of the anions is more effective in terms of changes in sigma and t(Na+) The percentage crystallinity and dielectric constant of the medium are also correlated with the observed effect. The electrolyte dissociation model has been applied to explain the composition-dependent behavior.